You are of course correct, but (a) that's not what the GP was implying since most non iTunes music players and all significant non-iTunes stores support MP3, (b) it doesn't matter to most users, and (c) Ogg Vorbis is only unencumbered to the extent that is too insignificant to represent a useful lawsuit target.
As for (c), AOL did legal research before publishing the Vorbis decoder for WinAmp, and Microsoft used Vorbis for various game titles (I'd guess they also did some legal research).
Of course, anyone can sue over anything, and keep you engaged in court for a long time, even without a good reason.
MP3licensing (or MPEG-LA for the newer stuff) doesn't indemnify licensees, as can be seen every year when Sisvel lets German customs confiscate media players on Cebit over MP3 patents not part of the pool.
